重载 && 重载递增递和减运算符

class Rule
{
private:
    double m_Length;
public:
    explicit Rule(double lg = 1.0) :m_Length{ lg }{}

    Rule &operator++();
    const Rule operator++(int);

    Rule &operator--();
    const Rule& operator--(int);

    void showRuleLength()
    {
        cout <<"长度："<< this->m_Length << endl;
    }
};

inline Rule& Rule::operator++()
{
    ++(this->m_Length);
    return *this;
}

inline const Rule Rule::operator++(int)　　//返回常量对象，不允许改变
{
    Rule rule{*this};　　　　 //利用复制构造函数建立对象

    ++*this;　　　　　　　　　　//因为前缀++已经重载了
    return rule;　　　　　　　 //返回对象的副本
}

inline Rule& Rule::operator--()
{
    --(this->m_Length);
    return (*this);
}

inline const Rule& Rule::operator--(int)
{
    Rule rule(*this);
    --*this;
    return rule;
}

int main()
{
    Rule a{ 4.0 };
    Rule b;
    b = a++;
    b.showRuleLength();
}